ACTG 362 - This study is designed to assemble and follow a cohort of patients who have, at any time in the past, had a CD4 count of <50/mm3, but who have sustained an increase to above 100/mm3, and to compare two strageties for the prevention of MAC disease and other infections. These strategies include weekly azithromycin (1200mg) versus placebo with a plan to institute open-label azithromycin in all patients who experience a sustained decline in CD4 count to below 50m/mm3 during follow-up.